Tech veterans Greg Cohn and Will Carter tried to develop a social platform that would let users establish virtual "office hours" for chatting with strangers and colleagues. The reception among beta testers was lukewarm. But one feature stood out: the ability to create temporary phone numbers that forward to one's mobile phone.

Cohn and Carter's beta testers had a range of uses for fleeting phone numbers that would mask their permanent digits. Among them: Craigslist sales, online dating and maintaining a public internet persona without giving away private coordinates.

"There are all these things in our lives that internet platforms and mobile operating systems are enabling. And the phone number was trapped in 1985. It hasn't gotten smart," says Cohn, a former senior director at Yahoo.

Realizing they were on to something, Cohn and Carter formed Ad Hoc Labs to develop Burner, a mobile app that doles out disposable phone numbers for calling and texting. A prototype they debuted at SXSW in March 2012 earned accolades. That August, the Los Angeles duo launched Burner for U.S. and Canadian iPhone users.

Silicon Valley seed capital started pouring in. By early 2013, Ad Hoc had raised approximately $500,000 in angel funds. In April 2013, the company launched an Android version of Burner. The app quickly became one of iTunes' top 10 downloaded utilities. Annual revenue is in the millions, says Cohn, Ad Hoc's CEO. He declined to give specific sales or download figures.

Users include entrepreneurs, salespeople, investors, bloggers, job hunters, lawyers, teachers--anyone who might balk at providing a private number to people with whom they must interact, Cohn says. Also boosting Burner's customer base: the ubiquity of web transactions among strangers through services such as Airbnb, Lyft and Etsy. "At some point, people do want to talk or text outside of those [services'] message boxes," Cohn says.

Burner is free to download and doesn't require a contract. The first disposable number is free and lasts for a week, five voice calls or 15 texts--whichever comes first. After that, users buy credits (three for $1.99, up to 25 for $11.99) to apply to various Burner "plans." For example, three credits buy two weeks, 20 voice calls or 60 texts. Phone carriers charge for Burner voice minutes used, but Burner text messages are on the house.

You can permanently ditch a Burner number at any time, rendering it out of service and banishing it from your phone history. You can also maintain multiple Burner numbers at once, give each a ringtone and name and archive specific conversations.

Burner isn't the only mobile tool of its kind, so to stay ahead of the pack, Ad Hoc relies on user feedback and frequent upgrades. Possible future features include creating message transcripts and saving, sharing or otherwise exporting conversations, Cohn says. Another possibility is for Ad Hoc to partner with online-dating, job-listing and classifieds platforms.

Fueling this progress is a $2 million financing round Ad Hoc announced last fall, led by venture capital firms Founder Collective and Venrock. "The goal is to innovate faster," says Cohn, who immediately began growing Burner's technical team with the funds.

Venrock vice president Marissa Campise (who sits on Ad Hoc's board) says that wresting control of phone numbers away from telecom carriers and into the hands of privacy-minded consumers was a long-overdue development. "The days of everyone having one single phone number that you use for everything, tied to one single device, are limited," she says. "We see Burner as being big on the scale of web-based e-mail and big on the scale of everyday usefulness--meaning everyone who uses a cell phone should use Burner."